Conventional spray guns essentially consist of a base body that features a handle and a head section and contains compressed air conduits, a nozzle set, a compressed air connection, a trigger, an air guidance system with an air valve, an air nozzle and a mechanism for adjusting the volume and the pressure of the air flowing through the compressed air conduits, as well as a material guidance system with a paint needle and a mechanism for adjusting the material volume. The spray gun head features a material-conveying region, through which the material to be sprayed flows from a spray medium inlet to a spray medium outlet that is typically realized in the form of a material nozzle. A material supply, for example, in the form of a reservoir or a supply line from an external material storage system is provided at the spray medium inlet. Conventional reservoirs consist, for example, of gravity-feed cups, suction-feed cups or laterally mounted cups. The pressure difference can be produced by means of a material conveying device or by means of air flowing past an opening on the material supply. All free-flowing materials such as, for example, paints, varnishes, adhesives or the like may be considered as spray mediums.
The compressed air required for the spraying process is supplied at the air connection that is arranged on or in the pistol grip. The air valve is opened by actuating the trigger up to a first pressure point. When the trigger is additionally pulled back, the paint needle is retracted from the spray nozzle. The spray medium then respectively flows out of the material nozzle due to the gravitational force or a pressure difference and is atomized by the compressed air exiting the air nozzle.
Spray guns of this type have proven themselves in practical applications for many decades. However, it is disadvantageous that they respectively require careful cleaning of the material-conveying regions after each use and before each material change because clogging of said regions, as well as a contamination of the spray medium, could otherwise occur. In the prior art, this problem is solved by utilizing a material guide in the form of a cartridge, i.e., in the form of an exchangeable insert or exchangeable spray medium guide unit, that preferably consists of a disposable article. For example, DE 3016419 C2 discloses an advantageous spray gun of this type with a holding region and with a head that is equipped with a cartridge, wherein the cartridge features an inlet region for a material-conveying conduit that ends in an outlet region, wherein the inlet region of the cartridge is connected or can be connected to a reservoir for the material to be sprayed, and wherein the cartridge preferably guides at least one material-conveying component of the spray gun. This spray gun has a head that is divided into two parts, and features a rear region with respect to the spraying direction and a front region with respect to [as] the spraying direction. The rear end of the front region of the two-part head is equipped with a plug-type fitting for a cartridge with a tubular material-conveying conduit that extends in the direction of the spray jet, and in the interior of which a nozzle needle or paint needle is respectively arranged. The nozzle needle can be moved back and forward in the direction of the spray jet by means of a lever and spring mechanism such that the material to be sprayed can pass the nozzle arranged in the outlet region. The cartridge is held in the head by means of pin connections. After its use, the pin connections can be disengaged and the two head regions can be pivoted apart from one another such that the cartridge including the paint needle can be removed from the head and then discarded. A new cartridge can then be respectively fixed on or in the spray gun. In this way, cleaning of the material-conveying regions of the spray gun is not required. However, the pin connections are relatively complicated, as well as difficult to manufacture and disengage, and also do not always ensure a flawless operational reliability.
Another spray gun with an exchangeable cartridge is described in DE 10 2004 027 789 A1. The object of this publication is a two-part spray gun, in which each of the two parts features a recess for accommodating an exchangeable paint medium guide unit. The exchangeable paint medium guide unit is inserted into the receptacle of the first gun part. The second gun part is subsequently attached to the first part and fixed with a screw. Due to these numerous preparatory steps, the set-up of the spray gun is very elaborate and time-consuming. The two-part design of the gun furthermore requires immense additional effort during the manufacture because the two gun parts are not identical such that two production lines are required. This increases the manufacturing costs of the spray gun. In addition, it is also difficult to seal the gun cavities relative to the outside air.
Another embodiment of a spray gun with an exchangeable cartridge is disclosed in WO 2009/015260 A2. In this case, the gun essentially also consists of two parts, namely a front and a rear part that are connected to one another by means of a hinge. In order to insert the cartridge, the front part is pivoted downward such that the cartridge receptacle is exposed. After inserting the cartridge, the front part is once again pivoted upward and connected to the rear part by means of a spring-loaded latch. Although this allows a faster insertion of the cartridge into the gun than in the above-described prior art, the quality of the hinge, particularly its accuracy and its stability, is subject to very strict requirements. The manufacturing effort is therefore very high in comparison with a conventional spray gun and the production is associated with substantial additional costs.